Image guided radiation therapy apparatus

ABSTRACT

An IGRT apparatus comprising a medical imaging device ( 1 ) integrated with a linear accelerator ( 3, 4 ), the linear accelerator ( 3, 4 ) configured for emitting a radiation beam which is shaped by a beam shaper ( 8, 17 ), wherein the position of the beam shaper ( 8, 17 ) is adjustable between a first position and a second position, wherein the first position is a treatment position and the second position is a non-treatment position and wherein the IGRT apparatus comprises a gantry ( 2 ) and wherein the first position is within the gantry ( 2 ) and the second position is removed from the gantry ( 2 ).

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 14/524,660, filed Oct.27, 2014, and claims the benefit of GB 1319001.2, filed on Oct. 28,2013, both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to image guided radiation therapy (IGRT)apparatus. More particularly the invention provides an IGRT apparatus inwhich components can be conveniently and efficiently maintained andrepaired.

BACKGROUND OF THE INVENTION

Radiation therapy is a localised treatment designed to treat anidentified tissue target (such as a cancerous tumour) and spare thesurrounding normal tissue from receiving doses above specifiedtolerances thereby minimising risk of damage to healthy tissue. Prior todelivery of radiation therapy, an imaging system can be used to providea three dimensional image of the target from which the target's size andmass can be estimated and an appropriate treatment plan determined.

Many factors may contribute to differences between the dose distributiondetermined in the treatment plan and the delivered dose distribution.One such factor is an inconsistency between the patient position at theimaging stage and the patient position in the radiation treatment unit.

Image guided radiation therapy (IGRT) is known. The method involves theuse of an imaging system to view target tissues whilst radiationtreatment is being delivered to the target tissue. IGRT incorporatesimaging coordinates from the treatment plan to ensure the patient isproperly aligned for treatment in the radiation therapy device.

Various medical imaging technologies are used to identify target tissuesin radiation therapy planning and IGRT. These include (withoutlimitation); Computed Tomography (CT), Positron Emission Tomography(PET) and Magnetic Resonance Imaging (MRI). MRI is ideal for on-lineposition verification during radiotherapy, it is able to make fast 2Dimages of soft tissues with orientation along and perpendicular to thefield axis, allowing imaging at critical locations which are definedduring the treatment planning procedure. MRI also provides excellentcontrast between tissue types giving a sharp image of the target.

The Applicant's prior published international patent application no.WO03/008986 describes a device for use in IGRT which includes thefunctions of an MRI device in a radiation therapy treatment apparatusand proposes technology for overcoming the problems in doing so.

The large scale of these combined devices will be appreciated. Suchdevices are typically of the order of 2-3 meters in diameter and theyweigh several tons. It will be appreciated they cannot be easilytransported or manoeuvred for maintenance and repair.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an imageguided radiation therapy apparatus comprising a medical imaging deviceintegrated with a linear accelerator, the linear accelerator configuredfor emitting a radiation beam which is shaped by a beam shaper, whereinthe position of the beam shaper is adjustable between a first positionand a second position wherein the first position is a treatment positionand the second position is a non-treatment position.

The inventors have recognised that the cumbersome proportions of acombined medical imaging and radiation therapy treatment device presentmaintenance and repair engineers with a challenge in accessing componentparts of the device for service.

Preferably, the second position is a service position.

Preferably, the IGRT apparatus comprises a gantry and the first positionis within the gantry and the second position is removed from the gantry.

Whilst the beam shaper component must be carefully aligned fortreatment, its position within the gantry is inconvenient for thepurposes of servicing. As one of the more complex components of theapparatus, it is important the beam shaper can be readily accessible formaintenance purposes. The provision of adjustment means for adjustingthe position of the beam shaper enables the beam shaper to be movedbetween an operational position and a service position, the serviceposition being much more easily accessible for the service engineer.Optionally, the device provides for a range of servicing positions.

Preferably, the position of the linear accelerator is moveable with thebeam shaper between the first and second positions.

The radiation beam emitter of the linear accelerator is transportedaround the target tissue by means of a gantry. When in operation, thebeam shaper must be positioned adjacent the radiation beam emitterwithin the gantry.

The beam shaper is typically a multi-leaf collimator (MLC). MLCcomprises multiple inter-engaging metal leaves which can each be movedindependently by means of multiple electro-mechanical positioningmechanisms.

The medical imaging device is desirably an MRI device. Since suchdevices generate a very strong magnetic field it is advantageous todistance a predominantly metal component such as an MLC from themagnetic field for servicing since any ferromagnetic material in the MLCwill be drawn to the magnetic field potentially resulting in damage ordisassembly of sub-components.

Adjustment of the beam shaper position can be achieved by means of anadjustment arm to which the beam shaper is mounted and a linkageconnecting the adjustment arm to a fixed body and operable to move thebeam shaper between the first and second position. For example, thefixed body might be the wall, floor or ceiling of a room in which theIGRT apparatus is installed. Alternatively the fixed body might comprisea support beam fixed to any of the walls, floor or ceiling of a room inwhich the IGRT apparatus is installed. In another alternative, the fixedbody is a gantry or framework of the IGRT apparatus itself.

The adjustment arm may be adjusted manually or by a mechanical orelectro-mechanical actuation means.

In some embodiments the linkage comprises a pivot operable to pivot thebeam shaper from a position within the gantry to a position removed fromthe gantry.

In such embodiments, the beam shaper can be caused to travel through asimple arc from the first to the second position and desirably also inreverse from the second back to the first position. The pivot cancomprise a simple hinge located at or adjacent a first end of theadjustment arm distal from a second end to which the beam shaper ismounted.

Actuation means may comprise any conventional mechanical orelectro-mechanical means; for example (but without limitation) ahydraulic or pneumatic system may be used. In another alternative, oneor more electrically operated actuators may be used. The actuators maycomprise rotary actuators, linear actuators or a combination thereof.The actuation means may further comprise a gearing system to facilitateleverage of the heavy components. Actuation means may be removablyattachable to the adjustment arm or may form an integral part of thearm.

In more complex embodiments, the linkage may comprise a multi-axisjoint. A multi-axis joint allows the arm to be pivoted as describedabove but also permits rotation of the adjustment arm about its own axisallowing greater manoeuvrability in positioning the beam shaper forservicing.

The adjustment arm may be provided with one or more joints operable topresent the beam shaper in an increased number of positions andorientations. Joints in the adjustment arm may comprise simple hingejoints, multi-axis joints or any combination thereof.

The adjustment arm may incorporate a linear actuator allowing the lengthof the arm to be adjusted thereby providing further flexibility in thepositioning of the beam shaper when removed from the gantry.

A variety of potential configurations for IGRT apparatus in accordancewith the invention are possible. For example, the imaging device couldbe an MRI device of an open ring configuration or a drum configuration.An open system may require more sophisticated engineering but mayprovide benefits to the subject in providing for less intimidating, morecomfortable treatment. In such a design, an open ring MRI system isintegrated with a rotating linear accelerator mounted on an additionalring. The additional ring may also support a beam stopper and amegavoltage imaging system.

Preferably the apparatus is configured such that magnetic imaging deviceand the linear accelerator may be operated both independently andsimultaneously.

Desirably the magnetic imaging device and linear accelerator arearranged to share an isocentre.

A preferred and probably more economical design solution may use a doseddrum design based on the conventional drum MRI design.

Active or passive magnetic shielding in the integrated system mayprovide a minimal field strength at the mid plane around the MRI magnet.This shielding can prevent magnetic distortion of the accelerator tubeand will also assist in minimising disturbance of the other acceleratorsystems in the dose proximity of the MRI system. Inclusion of theshielding results in a system necessarily of wider diameter than aconventional system and thus in a larger distance between isocentre andfocus. Alternatively the magnets can be designed in order to minimisethe field strength at the point(s) in space where the accelerator willoperate.

Preferably, the IGRT apparatus comprises a light source for projecting alight beam through the beam shaper when the beam shaper is in the secondposition. This can be used to confirm configuration and correct workingof the beam shaper during servicing. For example, the light beam can beprojected onto a ceiling or other surface.

Preferably, the linear accelerator is positioned such that the path ofradiation from the linear accelerator to a patient is linear. Putanother way, it is preferred that the path of radiation is not bent;rather the radiation path passes directly from the linear accelerator,through the beam shaper and to the patient.

An embodiment of the invention will now be described with reference tothe accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows schematically an IGRT apparatus.

FIG. 2 shows in two orthogonal views (a) and (b), a beam shaper mountedon an adjustment arm and accompanying actuation means for actuating theadjustment arm in accordance with one embodiment of the invention.

FIG. 3 shows the components of FIG. 2 arranged in an IGRT apparatus inaccordance with an embodiment of the invention.

FIGS. 4a and 4b show the inclusion of a light source for projecting alight beam through the beam shaper.

DETAILED DESCRIPTION OF DRAWINGS

As can be seen from FIG. 1, an integrated device is provided in a doseddrum arrangement which comprises an inner MRI portion 1 and an outergantry portion 2 which incorporates the linear accelerator having a headincluding a radiation gun 3, acceleration tube 4 and an X-ray emissiontarget (not shown). The resultant radiation is used to bombard a target6 in a body 7 contained in the bore of the gantry portion 2. A beamshaper 8 uses data from the MRI to focus the radiation beam emitted bythe linear accelerator onto the target 6. The body 7 is introduced toand guided through the isocentre on a sliding table 9. In use, thegantry is rotated about the isocentre to enable bombardment of thetarget 6 from multiple directions. The table 9 may also be tiltable toexpose the target 6 to the direct line of the emitted beam in anotherplane.

FIG. 2 shows two orthogonal views of an adjustment arm 18 whichcomprises a mechanical arm 10 having a first end 11 which can beconnected to a framework in the gantry of a suitably arranged IGRTapparatus by means of a pivotal linkage passing through a bore 16passing through the end 11. A second end of the arm 10 embodies ahousing 12 which houses an MLC having a leaf driving section 13 andmultiple leaf section 17. An actuator 14 is operable to cause themechanical arm 10 to rotate about a pivot point at the centre of bore16. The assembly is powered by cabling 15.

FIG. 3 shows schematically an adjustment arm 18 pivotally mounted in thegantry portion of an IGRT apparatus of substantially similar design tothe apparatus shown in FIG. 1.

When it is desired to access the MLC 17 for maintenance or repair, thegantry is rotated to position the MLC at an appropriate height for theservice engineer. One suitably positioned, the actuator 14 is operatedto rotate the mechanical arm about the pivotal linkage through bore 16allowing the assembly to be tilted outside of the outer circumference ofthe gantry 2 and the MLC revealed to the engineer in a safe andconvenient position a good radial distance from the magnetic fieldpresent in the MRI portion 1.

Desirably the assembly is lockable in position in the gantry whenradiation treatment is being delivered. This may be achieved byincorporating a locking mechanism into the actuator or linkage. In analternative, a lockable panel is provided on an outer circumference ofthe gantry 2 for containing the assembly 18 during delivery of radiationtreatment.

With reference to FIGS. 4a and 4b , the IGRT apparatus may include alight source 19 for projecting a light beam 20 through the beam shaperwhen the beam shaper is in the second position. This can be used toconfirm configuration and correct working of the beam shaper duringservicing. For example, the light beam 20 can be projected onto adetector 21 which is connected to calibration circuitry 22.

With particular reference to FIG. 4b , the light source 19 is bouncedoff a mirror 23 so that it follows the same path as radiation from theradiation source 24 through the leaves 25 of the MLC.

As will be evident from FIG. 4b , the radiation source is provided inline with the subject to be treated such that there is no need for abending magnet.

Other embodiments and simple design variations of the embodimentsdisclosed herein will no doubt occur to the skilled addressee withoutdeparting from the true scope of the invention as defined in theappended claims.

The invention claimed is:
 1. An image-guided radiation therapy (IGRT)apparatus, comprising: a medical imaging device integrated with a linearaccelerator, the linear accelerator configured for emitting a radiationbeam which is shaped by a beam shaper; and a gantry configured to rotatethe emitted radiation beam about an axis, wherein the beam shaper ismounted to an adjustment arm configured to adjust the beam shaperbetween a first position and a second position, and wherein the medicalimaging device is an MRI device generating a magnetic field, and thesecond position is a radial distance away from the magnetic field suchthat a magnetic field strength generated by the MRI device at the secondposition is lower than a magnetic field strength generated by the MRIdevice at the first position.
 2. The IGRT apparatus as claimed in claim1, wherein the first position is a treatment position, and the secondposition is a service position.
 3. The IGRT apparatus as claimed inclaim 1, wherein the position of the linear accelerator is moveable withthe beam shaper between the first and second positions.
 4. The IGRTapparatus as claimed in claim 1, wherein the beam shaper is a multi-leafcollimator.
 5. The IGRT apparatus as claimed in claim 1, wherein theadjustment arm is connected to a fixed body through a linkage andoperable to move the beam shaper between the first and second positions.6. The IGRT apparatus as claimed in claim 5, wherein the fixed body isintegral with the gantry, and wherein the linkage comprises a pivotoperable to pivot the beam shaper from a position within the gantry to aposition removed from the gantry.
 7. The IGRT apparatus as claimed inclaim 5, further comprising an actuator to move the adjustment armbetween the first and second positions.
 8. The IGRT apparatus as claimedin claim 7, wherein the actuator comprises a pneumatically orhydraulically operated component.
 9. The IGRT apparatus as claimed inclaim 8, wherein the actuator comprises at least one electro-mechanicalactuator.
 10. The IGRT apparatus as claimed in claim 9, furthercomprising a gearing system.
 11. The IGRT apparatus as claimed in claim5, wherein the linkage comprises a multi-axis joint.
 12. The IGRTapparatus as claimed in claim 5, further comprising a locking mechanismfor locking the beam shaper into position during delivery of radiationtreatment.
 13. The IGRT apparatus as claimed in claim 5, wherein theadjustment arm is provided with one or more joints operable to presentthe beam shaper in an increased number of positions and orientations.14. The IGRT apparatus as claimed in claim 5, wherein the adjustment armincorporates a linear actuator allowing the length of the arm to beadjusted thereby providing further flexibility in the positioning of thebeam shaper when removed from the operational position.
 15. The IGRTapparatus as claimed in claim 1, wherein the IGRT apparatus has a closeddrum configuration.
 16. The IGRT apparatus as claimed in claim 1,wherein the IGRT apparatus has an open ring configuration.
 17. Aradiation therapy apparatus for delivering radiation therapy to atarget, the apparatus comprising: a linear accelerator configured toemit, via a radiation beam emitter, a radiation beam along a beam pathtoward the target; an imaging device configured to obtain an image ofthe target; a beam shaper configured to shape the emitted radiation beamemitted toward the target; a gantry coupled to the linear accelerator,wherein the gantry is configured to rotate the radiation beam emitterabout an axis; and an adjustment arm connected to the gantry and to thebeam shaper, wherein the adjustment arm is configured to adjust the beamshaper between a treatment position and a non-treatment position, andwherein the medical imaging device is an MRI device generating amagnetic field, and the non-treatment position is a radial distance awayfrom the magnetic field such that a magnetic field strength generated bythe MRI device at the non-treatment position is lower than a magneticfield strength generated by the MRI device at the treatment position.18. The radiation therapy apparatus as claimed in claim 17, wherein theadjustment arm is connected to a fixed body through a linkage andoperable to move the beam shaper between the treatment and non-treatmentpositions.
 19. The radiation therapy apparatus as claimed in claim 18,wherein the fixed body is integral with the gantry, and wherein thelinkage comprises a pivot operable to pivot the beam shaper from aposition within the gantry to a position removed from the gantry. 20.The radiation therapy apparatus as claimed in claim 17, wherein theimaging device has an open ring configuration.